TREM2 and Alzheimer disease: The AD disease biomarkers glial fibrillary acidic protein (GFAP) and soluble triggering receptor expressed on myeloid cells 2 (sTREM2), measured in blood or cerebrospinal fluid (CSF), and translocator protein (TSPO) positron emission tomography (PET), an imaging marker, are associated primarily with innate immune responses.6, 7, 8